Randy hit the nail on the head. A modern PC with a medium to high end shader-based graphics card has an immense amount of video processing capability, far more than a typical DVD player. Every time the processing power goes up, there are more things we can do to improve video quality.

Historically the video I/O capabilities of PCs were below the best consumer equipment, particularly in terms of controlling noise, but (a) there has been a big push in raising the video quality bar over the last few years, and (b) moving to a digital video output (DVI or HDMI) takes away a lot of the noise issues anyways.

M60ti, VP180, QS8, M2ti, EP500, PC-Plus 20-39
M5HP, M40ti, Sierra-1
LFR1100 active, ADA1500-4 and -8